In the development of internal combustion engines, it is constantly sought to minimize fuel consumption and reduce pollutant emissions.
Fuel consumption is of particular importance in applied-ignition engines. This is the result of the traditional applied-ignition engine being operated with a homogeneous fuel-air mixture, in which the desired power is set by varying the charge of the combustion chamber by quantity regulation. Combustion chamber charge is altered by adjusting a throttle flap which is provided in the intake tract. The pressure of the inducted air downstream of the throttle flap can be reduced to a greater or lesser extent. At a constant combustion chamber volume, it is possible in this way for the air mass, that is to say the quantity, to be set by the pressure of the inducted air. However, quantity regulation by a throttle flap has thermodynamic disadvantages in the partial load range owing to throttling losses.
One approach for dethrottling the applied-ignition engine is the development of hybrid combustion processes. These hybrid combustion processes are based on the transfer of technical features of the traditional diesel engine, characterized by air compression, a non-homogeneous mixture, auto-ignition and quality regulation. The low fuel consumption of diesel engines results from the quality regulation, wherein the load is controlled by the fuel quantity injected.
The injection of fuel directly into the combustion chamber of the cylinder is therefore considered to be a suitable measure for noticeably reducing fuel consumption even in applied-ignition engines. A certain degree of dethrottling of the internal combustion engine can be achieved already by virtue of quality regulation being used in certain operating ranges. A direct-injection applied-ignition internal combustion engine is also the subject matter of the present disclosure.
With the direct injection of the fuel into the combustion chamber, it is possible in particular to realize a stratified combustion chamber charge, which can contribute significantly to the dethrottling of the applied-ignition engine working process because the internal combustion engine can be leaned to a very great extent by the stratified charge operation, which offers thermodynamic advantages in particular in partial load operation, that is to say in the lower and middle load range, when small amounts of fuel are to be injected.
A stratified charge is distinguished by a highly non-homogeneous combustion chamber charge which cannot be characterized by a uniform air ratio but which has both lean (λ>1) mixture parts and also rich (λ<1) mixture parts, wherein an ignitable fuel-air mixture with a relatively high fuel concentration is present in the region of the ignition device.
A relatively small amount of time is available for the injection of the fuel, for the mixture preparation in the combustion chamber, that is to say the mixing of air and fuel and the preparation including evaporation, and for the ignition of the prepared mixture.
Since a small amount of time is available for the preparation of an ignitable and combustible fuel-air mixture as a result of the direct injection of the fuel into the combustion chamber, direct-injection applied-ignition engine processes are significantly more sensitive to changes and deviations in the mixture formation, in particular in the injection and the ignition, than conventional applied-ignition engine processes.
The non-homogeneity of the fuel-air mixture is also a reason why the particle emissions known from the diesel engine process are likewise of relevance in the case of the direct-injection applied-ignition engine, whereas said emissions are of almost no significance in the case of the traditional applied-ignition engine.
In the case of the direct injection of fuel, problems are caused by the coking of the injection device, for example of an injection nozzle which is used for the injection. Small quantities of fuel which adhere to the injection device during the injection may undergo incomplete combustion under oxygen-deficient conditions.
Deposits of coking residues form on the injection device. Said coking residues may firstly disadvantageously change the geometry of the injection device and influence or hinder the formation of the injection jet, and thereby sensitively disrupt mixture preparation.
Secondly, injected fuel accumulates in the porous coking residues, which fuel, often toward the end of the combustion when the oxygen provided for the combustion has been almost completely consumed, then undergoes incomplete combustion and forms soot, which in turn contributes to the increase in particle emissions.
Furthermore, coking residues may become detached for example as a result of mechanical loading caused by a pressure wave propagating in the combustion chamber or the action of the injection jet. The residues detached in this way may lead to damage in the exhaust-gas discharge system, and for example impair the functional capability of exhaust-gas aftertreatment systems provided in the exhaust-gas discharge system.
Known are concepts which are intended to counteract the build-up of coking residues and/or which serve to deplete deposits of coking residues, that is to say to remove said coking residues from and clean the combustion chamber.
The German laid-open specification DE 199 45 813 A1 describes a method for operating a direct-injection internal combustion engine, in which method, upon the detection of deposits in the combustion chamber, for example on an injection valve, measures are implemented in a targeted manner for cleaning the combustion chamber, wherein the presence of deposits in the combustion chamber is inferred from a misfire detection system. Measures proposed for cleaning the combustion chamber include the targeted initiation of knocking combustion and/or the introduction of a cleaning fluid into the inducted combustion air. Both measures may contribute to fuel consumption and pollutant emissions. Knocking may be initiated by advancing spark timing from a current timing to past (more advanced than) a borderline threshold.
Proposed as a particularly advantageous cleaning fluid is water, the injection of which causes the combustion temperature to be lowered, as a result of which the emissions of nitrogen oxides (NOx) can be simultaneously reduced. The injection of water is however not suitable in partial load operation at low loads and low rotational speeds, because this harbors the risk of corrosion in the combustion chamber and in the exhaust-gas discharge system, and may yield disadvantages in terms of wear.
The European patent EP 1 404 955 B1 describes an internal combustion engine whose at least one combustion chamber has, at least in regions, a catalytic coating on the surface for the purpose of oxidation of coking residues. The catalytic layer is intended to promote the oxidation of coking residues, specifically to effect a fast oxidation of the carbon-containing lining at a boundary surface between the catalytic converter and lining at typical operating temperatures, and to thereby effect an early detachment of the deposit under the action of the prevailing flow. In this way, growth of the residues is reduced or even completely prevented.
A disadvantage of the method described in EP 1 404 955 B1 for the reduction of coking residues by oxidation is that, even when using catalytic materials, the minimum temperatures required for the oxidation may not be reached in partial load operation at low loads and low rotational speeds. It is however precisely these operating conditions of the internal combustion engine, specifically low loads and/or low rotational speeds, that promote, that is to say expedite, the formation of deposits of the type in question, and that necessitate a method for removing said deposits.
The German laid-open specification DE 101 17 519 A1 describes a method for operating a direct-injection internal combustion engine in which the inlet valve unit of a cylinder is purposely equipped to prevent the dissipation of heat, that is to say, is designed to increase the surface temperature in the region of the throat of the inlet valve. It is thereby sought to ensure that, at least in the throat, the high temperatures required for the depletion of coking residues are attained more often, or regularly, during normal operation of the internal combustion engine.
Nevertheless, that region in the load-rotational speed characteristic map in which the required temperatures are actually reached is merely widened, that is to say enlarged. The region in which the minimum temperatures of 380° C. required for the depletion of coking residues lies close or adjacent to the full-load line at high rotational speeds and high loads. Method-based measures for targetedly increasing the component temperature in other characteristic map regions are not implemented in DE 101 17 519 A1. Rather, it is relied upon that the required temperatures are generated of their own accord during normal operation of the internal combustion engine in corresponding regions of the load-rotational speed characteristic map.
In this respect, the method of DE 101 17 519 A1 also does not permit the depletion of coking residues, that is to say cleaning by oxidation, at low loads and low rotational speeds of the internal combustion engine.
The above-described problem takes on an even greater significance during the warm-up phase of the internal combustion engine, in particular directly after a cold start of the internal combustion engine, when the component temperatures are particularly low. This is because the low temperature level expedites the formation of coking residues and also makes the removal of said residues more difficult.
By contrast to the internal combustion engines described in EP 1 404 955 B1 and DE 101 17 519 A1, in which the component temperature is not or cannot be influenced, in particular raised, in a targeted manner by method-based measures, according to the disclosure, it is not relied upon that the temperatures required for the oxidation of coking residues are generated of their own accord during normal operation of the internal combustion engine. Rather, the component temperature of the injection device is influenced by the electric heating device, such that the depletion of coking residues can be controlled and performed in a targeted manner under all operating conditions.
The inventors have recognized the above described disadvantages and in the present disclosure describe systems and methods in which deposits of coking residues on the injection device may be removed in an effective and targeted manner under all operating conditions, in particular also during partial load operation.
In the internal combustion engine according to the disclosure, the temperature of the injection device may be raised in a targeted manner in the region of the catalytic coating by the electric heating device, such that the minimum temperatures required for the oxidation of coking residues may be attained or generated under all operating conditions, in particular also during partial load operation or at low loads and low rotational speeds.
Furthermore, the injection device of the present disclosure is equipped with an electric heating device which allows fuel to be introduced into the combustion to be pre-heated during the injection process. This advantageously assists the mixture preparation, in particular the evaporation of the injected fuel, and the initiation of the pre-reactions required for the combustion. The heating of the fuel by a heating device is particularly advantageous during the warm-up phase of the internal combustion engine after a cold start and in operating ranges with low temperatures, for example operating ranges with low loads and low rotational speeds.
Systems and methods are provided for reducing coking residues on an injection device of an applied-ignition, direct injection engine. An example system comprises an injection device; an electric heating device integrated with the injection device; a catalytic coating on a surface of the injection device; and a controller suitable to initiate a cleaning mode of the injection device wherein the electric heating device raises the temperature of the injection device. Heating the injection device allows coking residues on the injection device to oxidize in the presence of the catalytic coating.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Further, the inventors herein have recognized the disadvantages noted herein, and do not admit them as known.